1. Field of the Invention
The present invention relates to a semiconductor device having a shielding case on exterior thereof for prevention of influence of disturbance noise such as unwanted radiation noise (electromagnetic noise) and more particularly to a method for manufacturing such a semiconductor device, a method for fixing a shielding case, and electronic equipment having such a semiconductor device.
2. Description of the Related Art
As a semiconductor device of such a type as described above, there have been known photodetectors such as infrared remote control photodetector units and infrared communication devices (IRDA) that are used in household electric appliances, information communication devices (such as personal computers), and the like.
For example, in a receiver for remote control (which will be referred to as a “remote control photodetector unit”) for receiving infrared light signal transmitted from a device for remote control called a “remote control transmitter” or the like, the infrared light signal transmitted from the remote control transmitter is received by a photodetector device (photodiode chip, which will be referred to as a “PD chip”). Then the received infrared light signal is subjected to various types of signal processing such as amplification and waveform shaping by a signal control processing device (which will be referred to as an “IC chip”), and various audio visual instruments such as TV and VTR and office automation instruments such as personal computer are remotely controlled in response to the received signal.
The infrared light signal transmitted from the remote control transmitter is digital signal, which is received by a light receiving surface of the PD chip, and the received light signal is converted into weak electric signal. The weak electric signal is amplified by a factor of tens of thousands by an amplifier in the IC chip, and only required signal frequencies are extracted from the amplified electric signal by a filter circuit (band-pass filter (BPF)) for extracting only signal in a required frequency band. After that, the signal is outputted as digital waveform information similar to the infrared light signal by a detector circuit.
Such a remote control photodetector unit is formed by placement and fixation of the PD chip and the IC chip onto a lead frame and by subsequent sealing with molding resin. Among remote control photodetector units, there are multi-chip photodetector components in which outside of the molding resin is covered with a metal case and multi-chip photodetector components in which inside of the molding resin is covered with a lead frame. In general, remote control photodetector units require a remote control distance of not less than 10 meters. In any multi-chip photodetector component, signal amplification processing by a factor of tens of thousands is carried out for amplifying weak electric signal. Accordingly, not only signals but also noise components such as electromagnetic noise are amplified by the amplifier, so that a ratio of signal to noise (S/N ratio) cannot be well ensured. As a result, it is made impossible to extract only required signals. In order to prevent such a phenomenon, electromagnetic shielding is widely used with a metal shielding case or the like covering the PD chip, the IC chip, and vicinity thereof, as described above.
In a single piece of a product, the metal shielding case for covering the molding resin only covers the molding resin and is not connected to a lead in a GND terminal part of the lead frame. Therefore, it is common that on the occasion of mounting the chip on a board, a user connects the metal shielding case to the GND lead part of the lead frame through a pattern on the board so as to be at the same potential. In the past, there was a product having in itself electrical continuity between the GND lead part and the metal shielding case. This structure, however, requires additional work such as establishment of the electrical continuity by soldering and therefore causes cost increase. Thus products having in itself no continuity are dominant among discrete products in each of which a metal shielding case is installed.
Hereinbelow, a structure of the remote control photodetector unit will be described in accordance with FIG. 7. Onto a metal lead frame 1 (which is made of iron in majority of cases and will be referred to simply as a “lead frame” below) in FIG. 7, a PD chip 2 is bonded with insulative adhesive 3 and an IC chip 4 is bonded with conducting adhesive 5. The PD chip 2 typically has a PN junction structure and a reverse voltage is applied thereto in the case of the remote control photodetector unit, so that a potential occurs in an N electrode on the back face side of the PD chip. Therefore, insulation has to be maintained between the PD chip 2 and a PD chip mounting part of the lead frame 1 that is to have a GND potential by structural reason, and epoxy resin containing insulative filler is used for bonding between the lead frame 1 and the PD chip 2.
By contrast, either the conducting adhesive 5 or the insulative adhesive 3 will do for bonding of the IC chip 4 onto the lead frame 1 because a back face of the IC chip 4, which carries out signal processing at a front face side thereof, has nothing to do with signal processing. Typically used is conducting adhesive 5 (such as an adhesive in which Ag powder is mixed with epoxy resin) that is excellent in workability and that has a sufficient adhesive strength. An electrode part 6 of the IC chip 4 and an input/output lead part 7 of the lead frame 1 are connected to each other through a gold wire 8 (hereinbelow, referred to also as an “Au wire”) having a diameter of tens of micrometers. Similarly, connections through gold wires are provided between the PD chip 2 and an input/output lead part 7, between the IC chip 4 and other input/output lead parts 7, and between the PD chip 2 and the IC chip 4.
As shown in FIG. 8, the PD chip 2 and the IC chip 4 installed on the lead frame 1 as described above are sealed to be enclosed with thermosetting resin 9 (hereinbelow, referred to as a “mold sealing resin”) containing a dye allowing infrared rays to pass therethrough and blocking visible radiation. The lead frame 1 exposed from the mold sealing resin 9 is subjected to resin deburring, tie bar cutting, lead cutting, and soldering. Thus the input/output lead parts 7 of the lead frame 1 are separated so as to form individual input/output leads 12.
For the resin molded article having undergone soldering as described above, a casing process with use of the metal shielding case is carried out as follows (see JP 07-245420 A and JP 2000-236102 A, for example). As shown in FIGS. 9A and 9B, a multiplicity of resin molded articles are connected by a guide frame 11. In this state, as shown in FIGS. 10A and 10B, discrete metal shielding cases 10 are put on over the corresponding resin molded articles and are fixed by “crimping.” In this manner, the mold sealing resin 9 is surrounded by the metal shielding case 10 so that resistance to electromagnetic noise is ensured. Finally, the guide frame 11 is cut and thus a discrete article state is attained as shown in FIGS. 11A through 11C.
For production of electronic components, accommodation to automatic manufacturing equipment and overseas development of production have become typical with efficient production of the remote control photodetector units. The method of casing with the metal shielding cases for the remote control photodetector units (the method for fixing the shielding cases 10 to the resin molded articles in FIGS. 10A and 10B), however, is inefficient in that separate shielding cases 10 are mounted on each of the multi-connected resin molded articles, as described above. For more efficient production of the remote control photodetector units, accordingly, establishment of an efficient casing method with the metal shielding cases is required.